Manufacture of pencils



United States atent MANUFACTURE OF PENCILS Paul Pischel, Hanuover,Germany No Drawing. Application July 23, 195 Serial No. 445,477

Claims. (Cl. 18-475) The invention relates to a method of manufacturingwriting cores and is particularly useful in preparing writing cores foruse in mechanical pencils or for enclosure in wooden sheaths and thelike.

In the general common manufacture of writing cores, a pasty mass of highconsistency is extruded under high pressure through a nozzle in the formof a strand and the strand-like core still having a high content ofmoisture is laid out on boards or like supports in the desired straightform. The moist and still soft strand upon emerging from the extrusionpress is still capable of being molded by hand and this characteristicis taken advantage of in the final shaping of the strand hereinafteralso referred to as straightening the core.

The freshly extruded strand has usually a moisture content of to 30% byweight, depending upon the nature of the core mass and other factors orproduction. In order to remove or reduce this high moisture content thestrand has to undergo a drying process while in its final form intendedfor use to reach a state of final dryness. Such drying step is timeconsuming and required careful handling of the boards in an effort tomove the cores when they are still susceptible to deformation. Theproblem of drying can be alleviated only to a certain extent as the coremust undergo a slow drying for days and sometimes weeks in order to bebreak-resistant. An accelerated drying produces a core that may readilysplit. Furthermore, when straightening the freshly extruded strand orcore by hand, the core is often flattened or otherwise deformed bymanipulation and such deformities when reaching 3% of the diameter ofthe core make the core unsuitable for use in mechanical pencils in whichinaccuracies in diameter of the core should not approximate 2%.

Manual operations have been found of advantage in the production ofcolored writing cores as distinguished from graphite cores commonlyreferred to as lead. In the manufacture of colored cores the strandemerging from the press is guided and supported by hand to minimizedeformation and tearing particularly when producing cores having adiameter of l to 0.6 millimeter. Great skill is required in laying outsuch extra thin cores on boards.

It is common practice to pass the straightened core through variousdrying chambers or drying stages and to expose the cores to drying airof less moisture content.

A uniform and careful drying process of the cores while lying straighton the boards is advisable in order to avoid crumpling, chipping orbreaking of the core during writing. The straightening operation,especially for small sized cores, requires at least two thirds of thetime of extruding the strand and forming the straight moist core. Also,the experience has been made that, after the manual straightening, finaldrying and cutting, up to 30% of the cores are defective and form scrap,particularly when small sized cores are involved.

According to a prior method cores have been produced from a compositionincluding principally clay, color pigment (which may be graphite) and abinder. A suitable binder is a water-soluble cellulose ether orderivative thereof, such as methyl cellulose. The binding agent iscontained in the composition mass in a pasty state, and in order tothicken the mass by evaporation of excessive moisture before extrusionof the mass it has been proposed to heat the mass. The cores producedfrom such a composition are very hard and do not give up sufficient-material when passed over a writing surface. Therefore,

the straight and already dried cores of a length in which they are to besold are impregnated with wax or fat by submerging the cores in a moltenbath of such wax or fat.

Cores having indelible writing characteristic do not re quire the lattertreatment.

According to a more common practice, the wax or fat is added to the massbefore its extrusion to form the core,

and the invention, in its preferred form, is particularly concerned withthis mode of producing the core.

It has been discovered that the dried, hard and rigid cores containing aWater-soluble cellulose ether or derivative thereof, can regain theirpliability by heating the dried core and this can be made use of tore-shape the dried core. The thus re-shaped core, upon cooling, becomesrigid again without having lost any of its previous qualities, includingbreak-resistance.

It is the broad object of the invention to take advantage of thisdiscovery and to improve on the manufacture of writing cores which dueto the inclusion of a watersoluble cellulose ether or a derivativethereof, become re-shapable by the application of heat.

It is a further object of the invention to postpone the step ofstraightening the freshly extruded strand until after the drying stepand thereby permit a continuous operation of the extrusion press andstoring of the freshly extruded strand for the drying process in a moreconvenient form, for instance in coils.

It is a still further object of the invention to heat the dried strandimmediately before its use in a machine for wrapping a compositionsheath about the core.

Other objects and features of the invention will become apparent fromthe following description.

A preferred method of carrying out the invention will now be described.A suitable composition mass containing, for example, by dry Weight, 20%china clay, 20% Ca stearate, 20% coloring matter or pigment, 20% wax orfat (Japan wax, stearic acid, petrol wax), and 20% methyl cellulose or amixture thereof with tragacanth and sufficient water (ti. 7 parts ofwater to one part of the cellulose content) to form a. pasty mass, isextruded continuously and the strand thus formed is coiled in spiral or8-form or collected in any other suitable manner for storing and drying.According to the invention, the dried strand of great length is heatedto become soft and pliable again and in its pliable state isstraightened preferably by a suitable machine whereupon the thusstraightened strand or core is permitted to cool and harden again.

Although the previously mentioned binding agent as such does not exhibitthe characteristic of melting or being thermoplastic under heat, itappears that the extruded and dried strand becomes thermoplastic.Whatever the explanation may be, the thermoplastic characteristic of thealready dried core of a suitable composition such as mentioned above hasheretofore not been taken advantage of and, to my knowledge, was notexpected.

The method of the invention just described permits an extrusion of anydesired length of strand at great speed unhampered by conditions imposedby short lengthproduction. The thus produced strand has a uniformdensity and therefore an improved quality. An extrusion nozzle can beconveniently placed in an opening preferably at the top of a containerwhich is relatively moved for coiling the strand therein.

The container may be constructed as a drying chamber for receiving andcirculating therein drying air, or as a heating vessel for drying thestrand by convection, if desired, with the assistance of vacuum, byhigh-frequency electric current or infrared heat, or the container assuch may be placed with other containers in a drying chamber.

When heating again the dried and cooled strand to make the strandpliable again the container may serve as suitable means for submergingor exposing the strand to a heating medium. The heating may be carriedout in stages so that the strand will have an optimum degree ofpliability during uncoiling and during the subsequent straighteningoperation. Cooling of the straightened core can be accelerated toshorten the cooling period to a few seconds.

It has been found that heating the strand to about 50 C. or more causessutficient pliability and softening for the straightening operationwhich can be combined with cutting the core to desired lengths. The timeof heating the strand can be reduced to two to three seconds by usinghigher temperatures, for instance of 70 to 80 C.

It has also been found that the step of heating the dried coil can becombined with the impregnation of Wax in the previously mentioned methodaccording to which cores produced from a composition mass not containingthe wax are dried and the dried cores are impregnated with wax. Theaforementioned advantages remain.

It is also a feature of the present invention to combine the re-heatingof the already dried core with a manufacture of sheath pencilssubstantially as disclosed and described in US. Patent 1,937,104.According to this disclosure a pliable moisture-containing strand is fedthrough a nozzle forming a mandrel in the outlet of an extrusion press,the cross section of the outlet determining the form of the pencilsheath. A composition mass, f.i. of the self-hardening type, is pressedthrough the outlet while the core advances through the nozzle to form asheath pencil in a single operation. The invention is not concerned withthe mode of manufacture itself and, therefore, an illustration of themachine is not considered necessary.

The pencil stock thus produced is still in a plastic state and hardeningof the encased core tends to a shrinkage of the core diameter whichdiffers from the shrinkage of the sheath. The result of drying thesheath and core simultaneously invariably results in a loosely encasedcore. This disadvantage is avoided by the invention by feeding a driedcore in a state of final dryness made pliable by heating, through theinternal nozzle, whereby shrinkage of the composition during drying ofthe plast1c pencil stock causes a firm grip of the sheath on the alreadydry core.

While I have described a preferred form of the invention, I do not wishto be limited thereby; various changes may be made in the mode ofoperation, as disclosed and defined in the appended claims.

I claim:

1. In the method of producing writing cores for pencils from a pastycomposition mass consisting essentially of water, materials which inkind and amount are incapable of imparting pliability to a dried pencilcore under heat, and a water-soluble cellulose ether as binding agentwhich causes a finally dried rigid core to become pliable upon theapplication of heat, in combination with the steps of extruding thecomposition mass, collecting the extruded strand, and finally drying thestrand to rigidness, the steps of heating the thus dried strand to makesaid strand pliable, straightening the pliable strand and permitting thestraightened strand to cool and to form a rigid pencil core.

2. In the method of producing writing cores for pen cus from a pastycomposition mass consisting essentially of water, materials which inkind and amount are incapable of imparting pliability to a dried pencilcore under heat and a water soluble cellulose ether having thecharacterteristics of methyl cellulose as binding agent in the driedcore, water-soluble cellulose ether or a derivative thereof having thecharacteristic of methyl cellulose as binding agent in the dried core,the steps, in the sequence stated, of extruding the composition mass,collecting the extruded strand, finally drying the strand to rigidhardness, heating the finally dried strand to make said strand pliable,straightening the pliable strand and permitting the straightened strandto cool to form a rigid pencil core.

3. The method as defined in claim 2, in which the freshly extrudedstrand is collected and finally dried in coiled form.

4. The method as defined in claim 2, in which the freshly extrudedstrand is stored and finally dried in a container.

5. The method as defined in claim 2, in which the freshly extrudedstrand is finally dried while stored in a container, and the finallydried strand while in said container is heated prior to removing saidfinally dried strand from said container. 7

6. In the method of producing pencil cores from pasty composition massconsisting essentially of water, materials which in kind and amount areincapable of imparting pliability to a dried pencil core under heat, anda finely dispersed water-soluble cellulose ether as binding agent andthe dried, extruded mass having the characteristic of being pliable uponthe application of heat, the steps of extruding the composition mass,collecting the extruded strand, finally drying the strand to rigidhardness, heating the finally dried strand to make said strand pliable,straightening the pliable strand and permitting the straightened strandto cool to form a rigid pencil core.

7. The method as defined in claim 6, in which the freshly extrudedstrand is finally dried while stored in a container, and the finallydried strand while in said container is heated prior to removing saidfinally dried strand from said container.

8. A method of producing sheath pencils by extruding a pasty compositionmass adapted to form the encasing pencil sheath upon setting of the massabout a simultaneously advanced pencil core, including the steps offorming a supply of said pencil core in form of a strand by extruding apasty composition mass consisting essentially of water, materials whichin kind and amount are incapable of imparting pliability to a finallydried pencil core under heat, and a water-soluble cellulose ether or aderivative thereof as binding agent, collectmg the extruded strand incoil form, finally drying the coiled strand to rigid hardness, heatingsaid dry coiled strand to make the strand pliable and feeding thepliable strand through a nozzle in the outlet of an extrusion presswhile extruding said sheath composition about said finally dried strand,said strand being straightened by passing through said nozzle to formthe pencil core.

9. The method of producing writing cores for pencils from a pastycomposition mass consisting essentially of water, materials which inkind and amount are incapable of imparting pliability to a finally driedpencil core under heat, a water-soluble cellulose ether, the bindingagents being of a nature causing a core dried to hardness materialswhich in kind and amount are incapable of imparting pliability to afinally dried pencil core under heat, and water-soluble methyl celluloseas binding agent including the following steps in the stated sequence,extruding the composition mass, collecting the extruded strand anddrying the extruded strand in the absence of any straightening operationto slowly reduce the moisture content and to thereby obtain an extrudedstrand having the dryness and rigidness of a finished core, subsequentlyheating the strand to a temperature at which the strand becomes pliableand finally straightening and cooling the straightened strand.

References Cited in the file of this patent UNITED STATES PATENTS LoomisMar. 19, 1940 OTHER REFERENCES Cellulose and Cellulose Derivatives, byEmil Ott, pp. 790491, 2nd (revised) Printing, 1946. IntersciencePublishers, Inc., New York, NY.

